ce31880 did not fix doom-system-cpus on msys2 builds because the
function didn't handle integer return values from any of its code
paths (which formerly returned strings or lists).
Ref ce31880cccFix#5347
We only need this magic in CLI sessions. It's better to only use half
the CPUs in interactive sessions (if the user has enabled
comp-deferred-compilation for some reason).
Fixes#5042
+ enable lexical-scope everywhere (lexical-binding = t): ~5-10% faster
startup; ~5-20% general boost
+ reduce consing, function calls & garbage collection by preferring
cl-loop & dolist over lambda closures (for mapc[ar], add-hook, and
various cl-lib filter/map/reduce functions) -- where possible
+ prefer functions with dedicated opcodes, like assq (see byte-defop's
in bytecomp.el for more)
+ prefer pcase & cond (faster) over cl-case
+ general refactor for code readability
+ ensure naming & style conventions are adhered to
+ appease byte-compiler by marking unused variables with underscore
+ defer minor mode activation to after-init, emacs-startup or
window-setup hooks; a customization opportunity for users + ensures
custom functionality won't interfere with startup.
